何爲山脈數組?如果數組 A 是一個山脈數組的話,那它滿足如下條件:
首先,A.length >= 3
其次,在 0 < i < A.length - 1 條件下,存在 i 使得:
A[0] < A[1] < ... A[i-1] < A[i]
A[i] > A[i+1] > ... > A[A.length - 1]
方法1: 取中點mid和右邊半部分的中點mid1, 如果 mid位置的值大於mid1處的值,mid一定位於最大值的右邊;如果mid位置的值小於mid1處的值, mid一定位於最大值的左邊。
int findMaxIndex(int *arr, int size)
{
int left, right, mid, mid1;
left = 0;
right = size -1;
while(left < right)
{
mid = (right -left)/2 + left;
mid1 = (right - mid+1)/2 + mid;
if(arr[mid] < arr[mid1])
{
left = mid + 1;
}
else if( arr[mid] > arr[mid1] )
{
right = mid1 - 1;
}
else
{
right = mid1 -1;
}
}
return arr[left];
}
方法2:三分:
int findMax(int *data, int size)
{
int left = 0;
int right = size -1;
while( left < right)
{
int mid1 = left + (right - left)/3;
int mid2 = right - (right-left)/3;
if( data[mid1] >= data[mid2])
{
right = mid2-1;
}
else if(data[mid1] < data[mid2])
{
left = mid1 + 1;
}
}
return data[left];
}
方法三:比較mid和 mid+1處的值,判斷是在最大值的左邊或者右邊
int findMax(int *data, int size)
{
int left = 0;
int right = size -1;
while( left < right)
{
int mid = (right - left)/2 + left;
int mid1 = mid + 1;
if( data[mid1] - data[mid] > 0)
{
left = mid + 1;
}
else
{
right = mid1 - 1;
}
}
return data[left];
}